Preserve face ordering in OBJLoader and OBJMTLLoader.

OBJ loaders did not correctly preserve vertex and face list ordering and were creating duplicate vertex entries, rather than letting faces share vertices.
OBJLoader & OBJMTLLoader: Fixed sharing of Vector2 & Vector3 objects by UVs & normals.

Should bring the OBJ(MTL)Loader into compliance with #3762.
OBJ{MTL}Loader: Formatting & whitespace fixes.
Merge branch 'objloader-preserve-face-order' of https://github.com/algrs/three.js into dev